Rendering metal meshes taut



May 24, 1955 CASSMAN ET AL 2,708,788

RENDERING METAL MESHES TAUT Filed June 1, 1948 Invenfors:

Harry Cassman I Williavnfdward Jeljnes Reginald Sidne Web/ey By Wflfforney United States Patent RENDERING METAL MESHES TAUT HarryCassman, Harlington, William Edward Jeynes, Chalvey, Slough, andReginald Sidney Webley, Hayes, England, assignors to Electric & MusicalIndustries Limited, Hayes, England, a British company Application June1, 1948, Serial No. 30,234 Claims priority, application Great BritainJune 3, 1947 4 Claims. (Cl. 29-428) This invention relates to treatingthin metal meshes or foils so as to tauten them, the invention beingespecially but not exclusively applicable to the treatment of meshessuch as employed in the manufacture of television transmission tubes.

In the manufacture of television transmission tubes it is frequentlynecessary to employ a taut mesh of very fine pitch, as for example whenit is desired to evaporate material through the mesh on to a surface soas to form a multiplicity of discrete elements on the surface. Variousmethods have been proposed for rendering the mesh taut and according toone method a copper mesh is mounted on a frame having a coefficient ofthermal expansion slightly less than the material of the mesh, and it isthen heated in vacuo to a temperature of about 600 to 900 C., at whichtemperature the mesh contracts slowly in relation to the frame andbecomes taut, heating being stopped when a suitable degree of tension isattained, which can be judged by experience. It is believed that thecontraction of the mesh is due to recrystallisation of the mesh materialpromoted by the heat treatment. A similar method has been proposedemploying a silver mesh mounted on a frame composed of stainless steelor glass. In both cases, however, the method is fairly critical bothwith respect to the temperature to which the heating is carried, and thetime for which it is continued and the success of the method relies to agreat extent on the experience of the operator. It seems also that theheat treatment must be carried out in vacuo, though the reason for thisis not clear.

The object of the present invention is to provide an improved method oftreating thin metal meshes or foils so as to tauten them, with a view toproviding a method which is less critical and less dependent upon theexperience of the operator.

According to the present invention there is provided a method oftreating a thin metal mesh or foil, comprising the steps of extendingthe mesh or foil on a substantially rigid support, securing the edges ofthe mesh to the support with the portion of the mesh or foil between theedges thereof free from attachment to the support, applying in contactwith said metal mesh or foil a deposit of a metal predetermined to alloywith the metal of the mesh or foil to produce shrinkage thereof, andheating the mesh or foil to cause such alloying to occur with consequentshrinkage of the mesh or foil relative to the support.

The heating may be effected either in air or in vacuo and the alloyingof the metals is accompanied by the desired contraction or shrinkage ofthe mesh or foil, the said contraction or shrinkage occurring at a lowertemperature and more rapidly than would otherwise be the case, thealloying of the two metals being believed to be responsible for a morerapid crystal growth in the material of the mesh or foil as itre-crystallises due to the heat treatment. The method is therefore lesscritical with respect to temperature and time, and in addition, sincethe alloying of the metals is often accompanied 2,708,788 Patented May24, 1955 by a change in colour, the method may be less dependent uponthe experience of the operator. It is also found that in the case of amesh, for example, subsequent heating as occurs in the usual processesfor the manufacture of television transmission tubes is less harmfulthan in the case of meshes rendered taut by some methods such asemployed hitherto, since such subsequent heating does not produceappreciable slackening of the mesh.

In order that the said invention may be clearly understood and readilycarried into effect, the same will now be more fully described withreference to the accompanying drawing, in which one example of thepresent invention, applied to the treatment of a metal mesh for use inthe manufacture of a television transmission tube, is diagrammaticallyillustrated.

Referring to the drawing, a silver mesh 1 having for example'400filaments per linear inch and a thickness of 0.0004 inch (the mesh beingtherefore flexible) is cemented to a frame 2 of, for example, stainlesssteel, by applying a suspension of colloidal silver in oil to the edgesof the mesh, applying the mesh to the frame while the mesh is in anextended, that is a more or less taut condition, and subsequently dryingout the suspension by heat treatment so that the edges of the mesh areleft firmly adhering to the frame 2 by means of a thin layer of silver 3with the portion of the mesh between its edges free from attachment tothe frame as indicated in the drawing. The mesh may of course be securedto the frame in other suitable ways, for example by applying a nickeltape to the edges of the mesh and welding the tape to the frame throughthe interstices of the mesh. In the drawing the mesh and frame are shownin transverse section, and it will be appreciated that their relativedimensions are not shown in correct proportion. Before or after mountingthe mesh on the frame, the mesh is coated with a thin film of gold 4, ofa thickness, say, of 10- inches in the case of a mesh with thedimensions given, the film being applied by any suitable method, forexample by plating the gold on to the mesh or by sputtering orevaporating the gold on to the mesh. The mesh secured to the frame isthen heated either in air or in vacuo to a temperature of between 300and 500 C., the heating being continued until the alloying of the twometals is observed, accompanied by a tautening of the mesh. Whenalloying accurs the colour of the mesh changes from gold to a paleyellow. The invention has been described with reference to the treatmentof thin metal meshes so as to tauten them, but the invention can also beapplied to the treatment of metal grids or grills such as are employedin other forms of electron discharge devices, or to other arrays ofmetal filaments which require to be supported in a taut condition. It isto be understood therefore that the expression metal mesh used hereinand in the claims is intended to include such arrays of metal filaments.In addition the invention may also be applied where it is desired toprovide a metal foil supported in a taut condition. Furthermore themethod is not limited to the employment of a silver mesh or foil havinggold deposited on it, but it can be applied to other metal which willalloy together and produce shrinkage, for example it may be applied to anickel mesh or foil having copper deposited thereon.

We claim:

1. A method of treating a flexible metal mesh or foil structure suitablefor use in an electron discharge device to render it taut, comprisingthe steps of extending the structure on a substantially rigid support,securing the edges of the structure to the support with the portion ofthe structure between its edges free from attachment to the support,applying to the surface of said structure a deposit of a metalpredetermined to alloy with the metal of the structure to produceshrinkage of the structure, and finally heating the structure to causealloying of the metal of said structure with the deposited metal andconsequent shrinkage of the unattached portion of said structurerelative to said support.

2. A method of treating a flexible silver mesh or foil structuresuitable for use in an electron discharge device to render it taut,comprising the steps of extending the structure on a substantially rigidsupport, securing the edges of the structure to the support with theportion of the structure between its edges free from attachment to thesupport, applying a deposit of gold to the surface of said structure,and finally heating the structure to cause alloying of the silver of thestructure with said gold and consequent shrinkage of the unattachedportion of the structure relative to said support.

3. A method of treating a flexible silver mesh suitable for use in anelectron discharge device to render it taut, comprising the steps ofextending the mesh on a substantially rigid support, securing the edgesof the mesh to the support with the portion of the mesh between itsedges free from attachment to the support, applying a deposit of gold tothe surface of said mesh, and finally heating the mesh to a temperaturebetween 300 C. and 500 C. to cause alloying of the silver of the meshwith said gold and consequent shrinkage of the unattached portion of themesh relative to the support.

4. A method of treating a flexible silver mesh suitable Cit for use inan electron discharge device to render it taut, comprising the steps ofextending the mesh on a steel frame conforming to a closed figure,securing the edges of the mesh to the frame with the portion of the meshbetween its edges free from attachment to the frame, applying a depositof gold to the surface of said mesh, and finally heating the mesh tocause alloying of said silver and said gold and consequent shrinkage ofthe unattached portion of the mesh relative to said frame.

References Cited in the file of this patent UNITED STATES PATENTS1,106,516 Lachman Aug. 11, 1914 1,275,022 Harrison Aug. 6, 1918 1,747,84Schlenker Feb. 18, 1930 1,863,073 Smythe June 14, 1932 1,904,241Kammerer Apr. 18, 1933 2,162,808 Gallup June 20, 1939 2,330,202 BrennanSept. 28, 1943 FOREIGN PATENTS 475,393 Canada July 17, 1951 OTHERREFERENCES Barrett, Structure of Metals, page 201, McGraw-Hill BookCompany, New York, 1943. (Copy in Div. 3.)

